The packaging of the above-mentioned powdery materials and liquids requires the prevention of water vapor or oxygen transmission and the prevention of visible light ray transmission. In general, (1) a translucent packaging material formed of a laminate comprising wax-coated printed paper, aluminum foil provided on the back thereof, and a heat sealable layer such as an ethylene-acrylic acid copolymer or an ethylene-vinyl acetate copolymer provided on the back of the aluminum foil, or (2) a translucent packaging material formed of a laminate comprising a biaxially stretched polyethylene terephthalate film/an adhesive polyethylene film layer/aluminum foil/a biaxially stretched polypropylene film/a heat sealable polyethylene film has been used in the form of a carton box or a flexible packaging bag.
In general, the packaging bags for the above-mentioned powdery materials are first filled with contents such as tea, coffee beans and drugs, and then inspected to determine whether or not the contents are contaminated with foreign materials such as metal powders. Thereafter, opened portions of the bags are heat sealed, followed by shipment or storage.
However, the inspection with the bags opened results in giving an opportunity to contaminate the contents with dust and foreign materials. The market has therefore desired packaging materials which can be inspected for the inclusion of metal powders in contents after filling and heat sealing of the opened portions.
Further, the conventional packaging materials have the disadvantage that aluminum foil is left unburned after burning of the packaging materials, resulting in troublesome treatment thereof.